Revert "remove comments from pre-commit ci config"

This reverts commit 14eb1d8.

Author: TomNicholas

.pre-commit-config.yaml

@@ -1,3 +1,4 @@
+# https://pre-commit.com/
 ci:
   autoupdate_schedule: monthly
 repos:
@@ -7,10 +8,12 @@ repos:
       - id: trailing-whitespace
       - id: end-of-file-fixer
       - id: check-yaml
+  # isort should run before black as black sometimes tweaks the isort output
   - repo: https://github.com/PyCQA/isort
     rev: 5.10.1
     hooks:
       - id: isort
+  # https://github.com/python/black#version-control-integration
   - repo: https://github.com/psf/black
     rev: 22.10.0
     hooks:
@@ -23,16 +26,33 @@ repos:
     rev: 5.0.4
     hooks:
       - id: flake8
+  # - repo: https://github.com/Carreau/velin
+  #   rev: 0.0.8
+  #   hooks:
+  #     - id: velin
+  #       args: ["--write", "--compact"]
   - repo: https://github.com/pre-commit/mirrors-mypy
     rev: v0.982
     hooks:
       - id: mypy
+        # Copied from setup.cfg
         exclude: "properties|asv_bench|docs"
         additional_dependencies: [
+            # Type stubs
             types-python-dateutil,
             types-pkg_resources,
             types-PyYAML,
             types-pytz,
+            # Dependencies that are typed
             numpy,
             typing-extensions==3.10.0.0,
           ]
+  # run this occasionally, ref discussion https://github.com/pydata/xarray/pull/3194
+  # - repo: https://github.com/asottile/pyupgrade
+  #   rev: v1.22.1
+  #   hooks:
+  #     - id: pyupgrade
+  #       args:
+  #         - "--py3-only"
+  #         # remove on f-strings in Py3.7
+  #         - "--keep-percent-format"